This invention is related to the building envelope system design applicable to an exterior wall design such as a curtain wall system or a window wall system.
An exterior wall is formed by multiple wall units joined and sealed between two adjacent wall units in both horizontal and vertical directions. The major functions of an exterior wall include the aesthetic design provided by the project architect and the interior environmental protection design provided by the exterior wall system designer or supplier. It is well recognized in the industry that wind load resistance and water-tightness performance are the two most important functions in the interior environmental protection design. In opaque areas such as spandrel and column areas, the required functions of the completed wall include maintaining aesthetic performance in the exterior environment, providing thermal insulation, and providing a finished interior wall. A popular aesthetic design option for the opaque area is a hidden frame wall unit. There are two major types of opaque hidden frame wall units in today's market.
The first type of opaque hidden frame wall unit is a plate system consisting of a flat facing plate such as aluminum plate, ACM (aluminum composite material), stone, or glass and a perimeter frame to support the plate. The facing plate is structurally tied to the perimeter frame by a connecting means such as adhesive tape, structural silicone caulking, or welded studs, etc. for wind load resistance and sealed in between to provide water-tightness performance. In a conventional wall unit of this type, the connecting location is designed for sealing both air and water requiring a perfect seal. Because no seal can be truly perfect, such wall units are prone to water leakage problems.
In an Airloop System (U.S. Pat. No. 5,598,671, which is incorporated by reference), the water leakage problem is solved by creating a perimeter Airloop to isolate the air seal from the water seal. An Airloop System separates the air seal from the water seal, allowing for pressure equalization between the exterior air and the cavities in the perimeter frame. The equalized air pressure prevents water infiltration into the wall unit. However, the pressure equalization process takes a short period of time, and some incidental water infiltration may occur during that time. The infiltrated water will drain out of an Airloop system via air holes in the perimeter frame. In a hidden frame Airloop system, the water seal and the air seal are on the same vertical plane. Because of this, and the incidental water infiltration that may occur during the short time required for pressure equalization, the tolerable degree of seal imperfection in a hidden frame Airloop system is not as good as that for an exposed frame Airloop system (U.S. Pat. No. 7,134,247, which is incorporated by reference). Separation of the water seal and the air seal into different vertical planes in a hidden frame Airloop system, therefore, is desirable to enhance performance during the time required for pressure equalization.
In addition, quality control for the execution of the connecting means is critical to ensure structural safety against the facing plate being blown away by wind. Another structural problem with hidden frame wall units is that the thin facing plate is flexible and intermediate stiffeners are often required, creating a significant cost increase. To complete the wall system, thermal insulation with a vapor barrier is installed behind the exterior wall unit and a separate interior wall is installed to create the interior aesthetic design. Since the interior surface of the facing plate is in the interior air zone, in cold regions, quality control on the installation of the vapor barrier is critical for preventing interior water condensation on the interior surface of the facing plate. Interior water condensation on the opaque wall unit often leads to latent discovery of the serious problems of wet insulation and connection corrosion.
The second type of opaque hidden frame wall unit is a composite panel system consisting of two thin structural skins with structural insulating core sandwiched in between. The most popular product of this system is known as composite foam panel. The advantage of this system is the significant cost reduction due to the following factors: (1) elimination of perimeter frame due to the combination of structural and thermal insulating functions; (2) elimination of the separate interior wall if the interior panel surface is used as the finished wall surface. However, the system is prone to exterior aesthetic problems known as thermal bowing, thermal blistering and thermal rippling. Such systems also are prone to water leakage problems at the interface locations such as window perimeters.